title: Chemical speciation of arsenic-accumulating mineral in a sedimentary iron deposit by synchrotron radiation multiple X-ray analytical techniques.
abstract: The comprehensive characterization of As(V)-bearing iron minerals from the Gunma iron deposit, which were probably formed by biomineralization, was carried out by utilizing multiple synchrotron radiation (SR)-based analytical techniques at BL37XU at SPring-8. SR microbeam X-ray fluorescence (SR-mu-XRF) imaging showed a high level of arsenic accumulation in the iron ore as dots of ca. 20 microm. Based on SEM observations and SR X-ray powder diffraction (SR-XRD) analysis, it was found that arsenic is selectively accumulated in strengite (FePO4 x 2H2O) with a concentric morphology, which may be produced by a biologically induced process. Furthermore, the X-ray absorption fine structure (XAFS) analysis showed that arsenic in strengite exists in the arsenate (AsO4(3-)) form and is coordinated by four oxygen atoms at 1.68 angstroms. The results suggest that strengite accumulates arsenic by isomorphous substitution of AsO4(3-) for PO4(3-) to form a partial solid-solution of strengite and scorodite (FeAsO4 x 2H2O). The specific correlation between the distribution of As and biominerals indicates that microorganisms seems to play an important role in the mineralization of strengite in combination with an arsenic-accumulating process.
authors.affiliation: Department of Applied Chemistry, Faculty of Science, Tokyo University of Science, Kagurazaka 1-3, Shinjuku-ku, Tokyo 162-8601, Japan.
authors.forename: Satoshi
authors.initials: S
authors.lastname: Endo
authors.forename: Yasuko
authors.initials: Y
authors.lastname: Terada
authors.forename: Yasuhiro
authors.initials: Y
authors.lastname: Kato
authors.forename: Izumi
authors.initials: I
authors.lastname: Nakai
mesh_terms: D001151:Arsenic / Q000737:chemistry*; D002623:Chemistry Techniques, Analytical / Q000379:methods*; D005453:Fluorescence; D005583:Fourier Analysis; D019015:Geologic Sediments / Q000737:chemistry*; D007501:Iron / Q000737:chemistry*; D008855:Microscopy, Electron, Scanning; D008903:Minerals / Q000737:chemistry*; D011827:Radiation; D017356:Synchrotrons; D014961:X-Ray Diffraction; D014965:X-Rays
chemical_list: D008903:Minerals; D007501:Iron; D001151:Arsenic